Alloy



Patented June 23, 1936 UNITED STATES PATENT OFFICE ALLOY Roy E. Paine, Oakland, Calif., assignor, by mesne assignments, to Magnesium Development Corporation, a corporation of Delaware 1 Claim. The invention relates to magnesium base alloys and is directed to the development of alloys of this class which have good corrosion resistance, particularly in the cast and in the cast and heat treated condition.

The art of casting magnesium presents many practical difliculties which must be surmounted before the true commercial possibilities of magnesium castings can be fully realized. An alloy which is suitable for one application may be entirely unsuited to another and, as a consequence,

- it is frequently necessary to sacrifice desirable I5 portant characteristics.

characteristics of the alloy in order to more fully realize the advantages of some one or more im- Thus a compromise must quite frequently be made in order to approach in one alloy the optimum properties for a given application. For example, it may be found that. corrosion resistance can be sacrificed to a certain extent to obtain higher tensile strength, yield point, hardness, or similar mechanical properties."

Again, tensile strength may be sacrificed in order to obtain proper casting or working characteris-.

tics. It is an object of the present invention to develop magnesium alloys which will combine to a maximum degree the characteristics of corrosion resistance; favorable mechanical properties,

workability, susceptibility to improvement by heat treatment and adaptablity to sand casting.

A further object is the provision of magnesium alloys characterized by their susceptibility to be improved in mechanical properties by suitable thermal treatments. A further object is the provision of magnesium-base alloys characterized by good corrosion resistance in either the cast or in the cast and heat treated condition. A further object is the provision of magnesium alloys possessing excellent casting characteristics. A further object is the provision 'of magnesium-base alloys susceptible, within certain ranges, to mechanical deformation. 7

I have discovered that magnesium-base alloys containing from 0.5 per cent to 22 per cent of lead possess to an appreciable degree-the collective characteristics of alloys which are resistant to corrosion, alloys which may be readily cast, alloys which are susceptible to alteration of properties by thermal treatments, alloys having favorable mechanical properties, and alloys which, .within a restricted range, may be workedby extrusion,

forging, or other means of mechanical deformation.

In accordance with my invention lead may be present in amounts as low as 0.5 per cent. The

preferred casting alloys are those containing above about per cent of lead since it is in these alloys that the most pronounced combination of these difierent properties is obtained. The alloy may be worked by extrusion over a range of from about 0.5 per cent to about 22.0 per cent of lead. As an all around casting alloy I have found a magnesium alloy containing5 to 10 per cent of lead to be particularly adapted to general foundry purposes. Alloys falling within this preferred range of composition as well as other alloys comprised within the broader limits previously defined, have been subjected to severe tests designed to produce accelerated corrosion. Sand cast test bars poured in accordance with the best casting practice in the art were subjected to corrosion tests in the as cast and in the heat treated condition. In the example referred to the heat treatment was carried out at about 459 centigrade for about hours followed by quenching in water, and both heat treated and unheat treated test bars were subjected to that corrosion test which comprises alternately immersing the metal in, and removing it from, a 3 per cent sodium chloride solution for about 80 hours, a treatment referred to hereinafter as the alternate immersion treatment.

There are certain elements which may be added to the binary magnesium-lead alloys to particular advantage. Such, for instance, are the metals calcium, cadmium and zinc. These maybe added singly or in combination with each other, the zinc in amounts between about 1.0 per cent and 10.0 per cent, the calcium between about 0.1 per cent and 2.0 per cent, and the cadmium between about 1.0 per cent and 10.0 per cent. These alloying elements are substantial equivalents as indicated by their susceptibility to thermal treatment in magnesium-lead alloys. The calcium favorably affects the casting properties of the alloy without markedly decreasing its corrosion resistance. For instance, a magnesium alloy containing 21.4 per cent of lead and 0.25 per cent per cent of lead and 10.0 per cent of cadmium had in the sand cast condition a tensile strength of about 24,650 pounds per square inch and an elongation of about 9.8 per cent-in 2 inches. After a heat treatment of about 20 hours at about 450 AIter a thermal treatment of about 20 hours at 450 centigrade followed by an aging treatment '01 about 20 hours at 150 centigrade its strength also in surface hardness. An alloy oi this nature containingabout 8.0 per cent of lead and 0.85 per cent of manganese lost only 6 per cent of its original strength after 80 hours alternate imof alternate immersion, had lost about 60 per cent of itsstrength. V I, 7

Very favorable alloys can be compounded by using as a base an alloy of magnesium, lead and centigrade its tensile strength had increased to mersion in a 3 per cent aqueous solution of sodium 5 about 25,140 pounds per square inch and its chloride and in the solution heat treated conelongation to 10.3 per cent in 2 inches. After an dition lost only}? per cent of its strength in the alternate immersion corrosion test for 80 hours alternate immersion treatment. A magnesium the loss in strength was only per cent. A simialloy containing about 10.37 per cent of lead had lar result was obtained with amagnesium-base allost only about 10 per cent of its strength at the 10 loy containing about 5.3 per centof lead'andabout expiration of this period as compared with cer- 5.0 per cent of cadmium. An alloy of magnesium tain other commercial alloys, such as, for inwith about 5.0 per cent of lead and 5.0 per cent of stance, the well known magnesium alloy conzinc had in the sand cast condition a tensile taining about '7 per cent of aluminum and 0.4 per strength of about 23,370 pounds per square inch. cent of manganese which, at the en'dl'of 40 hours had increased to about 25,710 pounds per square inch. After an alternate immersion corrosion test aluminum and making additions thereto of at 0 of 80 hours the loss in strength was only 12 per least one of the class of metals tin, manganese cent. Another alloy of magnesium with about or zinc. The lead can be used in amounts from alloys (with or without calcium) tends to be about 0.5 per cent to about 22.0 per cent, the

5.2 per cent of lead and 3.2 per cent of zinc under aluminum from about 1.0 per cent to about 15.0

similar conditions lost only about 10 per cent after- 80 hours alternate immersion .in the corrosive per cent, the tin from about 1.0 per cent to 5 solution. As a preferred composition for alloys about 15.0 per cent, the manganese from about of this nature I advise (1) 5.0 per cent lead, 1.0 0.1 per cent to about 1.0 per cent, and the zinc per cent calcium, balance magnesium; (2) 5.0 from about 1.0 percent to about 10.0 per cent. per cent lead, 5.0 per cent cadmium, balance magj A sand cast alloy within this range had, in the nesium; (3) 5.0 per cent lead, 5.0 per cent zinc, as cast condition, a tensile strength of 27,500 30 balance magnesium. If more than one of the pounds per square inch and an elongation of elements calcium, cadmium, or zinc be present 5.7 per cent in 2 inches. After a thermal treatsimultaneously, I prefer not to exceed a total of ment of 16 hours at 315 centigrade, the alloy 10.0 per cent for these elements. had a tensile strength of 29,640 pounds per square One of the disadvantages of the alloys described herein which may affect their use in Some-of the heat treated specimens were then certain applications, particularly where high given an alternate immersion treatment for 40 strength is a leading or very materialconsiderahours and after the treatment the specimens tion, is the fact that the grain structure of these had a tensile strength of 28,413 pounds per square inch and an elongation oi 5.8 per cent in 2 40 inches, this alloy containing 5.0 per cent of aluminum, 5.0 per cent of lead, 0.4 per cent of coarse. I have found that the metals aluminum and silicon form a class of alloying elements which may be added to magnesium-lead alloys manganese and 2.0 per cent of. zinc. The loss andare substantially equivalent in this respect in strength on the corrosion treatment is ob that they materially refine the grain structure served to be less than 5 per cent as compared 45 of the alloy. Aluminum, for/instance, can be to about per cent with the commercial magneadded over a wide range, such as between 1.0 sium-aluminum-manganese alloy disclosed hereand 15.0 per cent; silicon may .be effectively inbefore which contains about 7 percent of alupresent for this purpose in amounts of about 0.1 minum and 0.4 per cent of manganese. As preinch and an elongation of 6.0 per cent in 2 inches. 35 I lead alloys inamounts between 0.I 'per cent and -'and 1.0 per centof tin.

The addition of lead tothe magnesium-aluminum-manganese alloys increases very considerably the corrosion resistance of these alloys, since to 2.0 per cent. When used in combination it is 'ferred compositions for alloys of this nature I 50 advisable that the total content of aluminum and adviseil) 7.0-per cent of lead, 7.0 per cent of silicon does not exceed 15.0 per cent. In the prealuminum, 2.0 per cent tin, balance magnesium; ferred practice of my invention I have found that (2) 7.0 percent lead, 7.0 per cent aluminum, 2.0 the best results are usually obtained when the per cent tin, 0.5 per centmanganese, balance aluminum is present in amounts between 5 and magnesium; (3) 7.0 per cent lead, 7.0 per cent 55 '10 per cent. a u 2.0 P t t 2.0 per cent zinc,

-As a preferred magnesium-lead-siliconcombalance magnesium. position I use a magnesium-base alloy containing Y'Iwo alloy compositions within this range which 7.0 per cent-of lead and 0.5 per cent of silicon. I have usedto advantageare as follows: A mag- As a preferred magnesium-lead aluminum alloy I nesium-base alloy containing 8.0 per cent of alu- 60 use a magnesium-base alloy containing'LO per minum, ,3.0 per cent of lead, 0.4 per cent of cent of lead and 5.0 per cent or aluminum. Whenv manganese, 1.0 per cent of zinc, and 3.0 per the aluminum and silicon are used in conjunc-' cent 01' tin; a magnesium base alloy containing tionI preferto use a total of about 5.0 per cent-of 8.0 per cent of aluminum, 1.0 p r cent of lead, aluminum and silicon combined, for instance 0.4 per cent of manganese, 1.0 .per cent of zinc,

1.0 per cent and has a stabilizing efiect upon the with theaddition of about 7 per cent of lead to alloy properties in that it raises the hardness slightly, does not materially decrease the corrosion resistance, and adds to the matrix of the alloy a hardening element which expresses itself not only in an increase in tensile strength but an alloy containing 7 per cent of aluminum and 1 per cent of manganese, the loss 01' strength after the alternate immersion test was only about Alloys of magnesium with lead, aluminum, and manganese have been disclosed hereinabove. I have discovered that if to a base alloy of magnesium-lead-aluminum-manganese I add one or more of the class of metals calcium or'cadmium, the resulting alloys become considerably more susceptible to variation of properties by thermal treatments and their hardness can be markedly increased by artificial. aging after thermal solution treatments. In these alloys the lead content cast specimen of a magnesium-base alloy con-' taining about 10.0 per cent of lead, about 7.0 per cent of aluminum, about 0.4 per cent of manganese, and about 5.0 per cent of cadmium, had in the cast condition a tensile strength of about 23,200 pounds per square inch. After a thermal solution treatment of 21 hours at about 430 centigrade the tensile strength of the alloy had j increased to about 36,000 pounds per square inch, a gain in strength of about per cent. The same alloy after the solution treatment had a Brinell hardness of about 61 and this hardness was raised to about 84 by an additional aging treatment of 20 hours at about 175 centigrade, the tensile strength increasing slightly to about 37,000 pounds per square inch.

Similarly a magnesium-base alloy containing about 5.0 per cent of lead, 7.0, per cent of aluminum, 10.0 per cent of cadmium, and 0.4 per cent of manganese had in the sand cast condition a tensile strength of about 24,000 pounds per square inch. After a thermal treatment of 21 hours at about ;430 centigrade the alloy had a tensile strength of about 35,000 pounds per square inch. An additional aging treatment raised the Brinell hardness of the alloy from about 61 to about 79.

Similarly, a magnesium-base alloy containing about 5.0 per cent of lead, 10.0 per cent of cadmium, 7.0 per cent of aluminum, 1.0'per cent of manganese, and 0.25 per cent of calcium had in the sand cast condition a tensile strength of 4 about 24,290 pounds per squarev inch. After a thermal treatment of 20 hours at about 430 centigrade this alloy had a tensile strength of about 33,200 pounds per square inch. After an' solution treatment of 21 hours at about 430 cen- 1 tigrade the alloy had a tensile strength of about ness was about 61.

- 36,030 pounds per square inch; the Brinell hard- After an additional aging treatment of about 20 hours at about centi- Another useful composition is attained by substituting about 1.0 per cent silicon for part or all of 'oxidizable metals.

magnesium-lead binary alloys, may be extruded grade its tensilestrength was about 37,010 pounds per square inch and its Brinell hardness about 84.

As a desirable alloy of this nature I advise 7.0 per cent lead, 7.0 per cent aluminum and 0.4

' per cent manganese. If more than one of the 5 combination decreases the linear shrinkage,-thus favorably affecting the casting properties, and also increases the corrosion resistance and raises the yield point of these alloys. In alloys of this 15 type the lead should range from 0.5 per cent to 22.0 per cent, the aluminum from 1.0 per cent to 15.0 per cent, and the silicon from 0.1 per cent to 2.0 per cent, but the total amount of aluminum and silicon should preferably not exceed 15.0 per 20 cent.

A useful alloy of this nature is a magnesiumbase alloy containing about 10.0 per cent lead, 8.0 per cent aluminum and 3.25 per cent zinc.

the aluminum.

An alloy similarly improved in casting properties, although not to such a decided extent, is one containing from about 0.5 per cent to 22.0 per 30 cent of lead, from about 1.0 per cent to' about 10.0 percent of zinc, and from about 0.1'per cent to about 2.0 per cent of silicon. A favorable al- 10y within this range is a magnesium-base alloy consisting of about 10.0 per cent of lead, about 35 3.25 per cent of zinc, and about 1.0 per cent of silicon, the balance being substantially magnesium. v

In making up alloys of the compositions disclosed hereinabove the alloys may be compounded by any of the methods known in the art. In casting the alloys recourse may be had to the protective measures disclosed in existing patents and the published literature relating to easily The alloys, especially the- 45 over the entire disclosed composition range, but other types of mechanical deformation such as rolling or forging should be carried on with due regard for the fact that as the percentage'of total added alloying elements increases, the necessity for precaution in working the alloy also increases.

It is my object to retain, as-far as possible, the advantages of the use of magnesium base, such as low specific gravity, while securing in addition theihereinabove disclosed benefits accruing from the'additions of the other alloying elements herein outlined. Accordingly, where in the appended claim the term magnesium-base alloy is used, it refers to an. alloy containing more than approximately 50 per cent of magnesium.

This application is a division of my copending application Serial No. 692,132, filed October 4, 1933.

I claim: 65

A magnesium-base alloy containing from about 0.5 to 22.0per cent of lead, from about 0.1 to 2.0 per cent ofcalcium, and from about 1.0 to 10.0 percent of cadmium, the balance being'mag- 

